The present invention relates to a valve actuation control apparatus for an internal combustion engine that controls valve parameters such as valve timing and valve duration of engine valves.
Variable valve actuation mechanisms that change the valve parameters of engine valves such as intake valves and exhaust valves according to the engine operating state have been made commercially available.
Variable valve actuation mechanisms include variable valve timing mechanisms. A variable valve timing mechanism changes the rotational phase of a camshaft relative to that of a crankshaft, thereby changing the valve timing of engine valves that are opened and closed by the camshaft.
Since such a variable valve timing mechanism is actuated by a drive source obtained from an engine power, such as hydraulic pressure and electricity, the mechanism is stopped when the engine stops. Therefore, the valve timing after the engine stops is the valve timing immediately before the engine stops, that is, the valve timing that has been set during the operation of the engine. The valve timing is not necessarily suitable for starting the engine. Thus, depending on conditions, starting performance of the engine could be degraded next time the engine is started.
Accordingly, Japanese Laid-Open Patent Publication No. 2002-161766 discloses an apparatus that performs a delay control for extending the period from when an engine stop request is made (when a driver turns off the ignition switch) to when the engine actually stops. After the delay control is started, the apparatus activates a variable valve timing mechanism to set the valve timing to predetermined valve timing suitable for starting the engine.
Meanwhile, Japanese Laid-Open Patent Publication No. 2001-263015 discloses a variable valve duration mechanism that is one type of a variable valve actuation mechanism driven by a drive source obtained from the engine power. The variable valve duration mechanism changes the valve duration of an engine valve that corresponds to a period during which the engine valve is open in accordance with the engine operating state.
Even such a variable valve duration mechanism is stopped when the engine stops. Therefore, the valve duration after the engine stops is the valve duration immediately before the engine stops, that is, the valve duration that has been set during the operation of the engine. The valve duration is not necessarily suitable for starting the engine. It is therefore desired that, after the delay control is started, the valve duration, which is changed by the variable valve duration mechanism, be changed to valve duration suitable for starting the engine.
When the valve timing and the valve duration are changed after the delay control is started in an internal combustion engine that is provided with a variable valve timing mechanism and a variable valve duration mechanism, the valve overlap is changed not only by changes in the valve timing, but also changes in the valve duration. This in some cases excessively increases the valve overlap during the execution of the delay control. An excessively increased valve overlap during the execution of the delay control is likely to cause a misfire. If the engine stalls due to such misfires, the delay control is interrupted.